Exhaust aftertreatment system

ABSTRACT

An apparatus for treating an exhaust gas feedstream from an internal combustion engine operating lean of stoichiometry comprises a particulate filter device comprising a porous substrate element having a hydrocarbon-selective catalytically reactive washcoat. The hydrocarbon-selective catalytically reactive washcoat comprises a silver-oxide catalytic material on an alumina-based washcoat. An injection device is operative to inject a hydrocarbon reductant upstream of the particulate filter device.

TECHNICAL FIELD

This disclosure is related to exhaust aftertreatment systems for internal combustion engines operating lean of stoichiometry.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

An internal combustion engine operating lean of stoichiometry can generate an exhaust gas feedstream including NOx emissions and particulate matter. There is a need for an exhaust aftertreatment system to manage the exhaust gas feedstream.

SUMMARY

An apparatus for treating an exhaust gas feedstream from an internal combustion engine operating lean of stoichiometry comprises a particulate filter device comprising a porous substrate element having a hydrocarbon-selective catalytically reactive washcoat. The hydrocarbon-selective catalytically reactive washcoat comprises a silver-oxide catalytic material on an alumina-based washcoat. An injection device is operative to inject a hydrocarbon reductant upstream of the particulate filter device.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGS. 1, 2, and 3 are schematic diagrams of engine and exhaust aftertreatment systems, in accordance with the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same, FIGS. 1, 2 and 3 schematically depict an internal combustion engine 10, control module (‘ECM’) 5, and embodiments of an exhaust aftertreatment system in accordance with the disclosure. Like numerals refer to like elements in FIGS. 1, 2, and 3 and the embodiments described herein.

The exemplary engine 10 comprises a multi-cylinder internal combustion engine operative in a repetitive combustion cycle which can comprise intake, compression, power, and exhaust strokes. The engine 10 is selectively operative at an air/fuel ratio that is lean of stoichiometry. The engine 10 can be one of a compression-ignition engine and a spark-ignition engine that is operative lean of stoichiometry. The engine 10 can operate in one or more combustion modes including compression-ignition, spark-ignition, and controlled auto-ignition combustion modes. The engine 10 includes a plurality of reciprocating pistons attached to a crankshaft, which is operably attached to a transmission and a vehicle driveline to deliver tractive torque thereto, none of which are shown. The engine 10 generates an exhaust gas feedstream containing constituents that can be transformed by the aftertreatment system, including, e.g., hydrocarbons (hereafter ‘HC’), carbon monoxide (hereafter ‘CO’), nitrides of oxygen (hereafter ‘NOx’), and particulate matter (hereafter ‘PM’).

The exhaust aftertreatment system comprises an integrated system for converting the constituents of the exhaust gas feedstream to other forms in the presence of catalytically reactive materials through oxidation and reduction processes. An exhaust manifold (not separately labeled) entrains and directs exhaust gas flow to the exhaust aftertreatment system. The exhaust aftertreatment system of FIG. 1 includes a catalytic device 14, an injection device 16, and a particulate filter device 20. The exhaust aftertreatment system of FIG. 2 includes catalytic device 14, injection device 16, particulate filter device 20 and a second catalytic device 24 downstream from the particulate filter device 20. The exhaust aftertreatment system of FIG. 3 includes particulate filter device 20 and second catalytic device 24 downstream from the particulate filter device 20. The aforementioned devices are preferably fluidly connected in series using pipes and connectors.

One or more sensing devices can be adapted to monitor the exhaust gas feedstream. The exhaust gas feedstream can be monitored at various locations in the exhaust aftertreatment system, with the locations shown being monitored by various ones of sensors 12, 18, 22, 26 and 28. An application of the exhaust aftertreatment system can include one or more of the sensors 12, 18, 22, 26 and 28. The sensors 12, 18, 22, 26 and 28 monitor parameters of the exhaust gas feedstream that can be correlated to constituents and/or temperature of the exhaust gas feedstream, and generate signals that are transmitted to the control module 5. This may include sensor 12 which monitors the exhaust gas feedstream output from the engine 10, preferably including one of NOx concentration and air/fuel ratio. Sensor 26 may monitor the exhaust gas feedstream downstream from the catalytic device 14, preferably including a parameter corresponding to one of NOx concentration, air/fuel ratio, and temperature. A specific embodiment of the system that includes sensor 12 may not include sensor 26. Sensor 18 may monitor the exhaust gas feedstream output from the catalytic device 14 and downstream of the injection device 16, preferably including a parameter corresponding to one of NOx concentration and temperature. Sensor 22 may monitor the exhaust gas feedstream downstream from the particulate filter device 20, preferably including a parameter corresponding to one of NOx concentration, temperature, and ammonia (NH₃). As shown in FIGS. 2 and 3, sensor 28 may monitor the exhaust gas feedstream downstream from the second catalytic device 24 in the second embodiment, preferably a parameter corresponding to one of NOx concentration, temperature, and ammonia. The control module 5 monitors the signals from the specific sensors 12, 18, 22, 26 and 28 and uses the signals to control of the engine 10 and the injection device 16, and to monitor operation of the engine 10, the injection device 16, the catalytic device 14, the particulate filter device 20, and the second catalytic device 24 to diagnose faults therein. Alternatively, a virtual NOx sensing system comprising an executable algorithm resident in the control module 5 can be used to determine the NOx concentration in the exhaust gas feedstream based upon engine speed/load operating characteristics.

The catalytic device 14 depicted in the embodiments shown in FIGS. 1 and 2 preferably comprises an oxidation catalyst. The catalytic device 14 is preferably constructed of a substrate (not shown) on which a washcoat and a catalytically reactive material, e.g., platinum or palladium, are applied. The substrate can be a metal foil device or a sintered ceramic device having a plurality of flow channels through which the exhaust gas feedstream can pass during operation of the engine 10. The coated substrate is assembled into a metallic structure that is an element of the exhaust aftertreatment system.

The injection device 16 depicted in the embodiments shown in FIGS. 1 and 2 preferably comprises a solenoid-operated fluid flow control valve that has a fluid outlet adapted to inject a hydrocarbon reductant into the exhaust gas feedstream downstream of the catalytic device 14 comprising the oxidation catalyst and sensor 26 and upstream of the particulate filter device 20. The injection device 16 is operatively connected to the control module 5, which controls timing and mass or quantity of the hydrocarbon reductant injected into the exhaust gas feedstream. The hydrocarbon reductant is preferably supplied from a fuel tank of the vehicle via a fluidic connection, none of which are shown.

The particulate filter device 20 comprises a filtering device that is coated with a hydrocarbon-selective catalytically reactive washcoat for NOx emission reduction. The filtering device traps particulate matter contained in the exhaust gas feedstream. There is a filter inlet 19 and a filter outlet 21. The particulate filter device 20 is constructed in a manner which causes the exhaust gas entering the filter inlet 19 to pass through a portion of the particulate filter device 20 to reach the filter outlet 21. By way of example, the particulate filter device 20 can include a multi-channel monolithic substrate element (not shown) constructed of a porous material. Each of the channels is either capped on an end proximal to the filter inlet 19 or capped on an end proximal to the filter outlet 21, with adjacent channels capped on alternate ends. By way of example, the porosity of the substrate element is about 40% to 55%, indicating that 40% to 55% of the volume of the substrate element comprises pores and not substrate material. The pores can have diameters that are less than about 3 microns on average. The porous material of the substrate element can be formed from ceramic material, e.g., cordierite that is extruded and sintered.

The porous material of the multi-channel substrate is coated with the hydrocarbon-selective catalytically reactive washcoat. The hydrocarbon-selective catalytically reactive washcoat, also referred to as an HC-SCR washcoat, includes a chemically reactive material that reacts with the injected hydrocarbon reductant to reduce NOx gases to N₂0. The hydrocarbon-selective catalytically reactive washcoat can comprise an alumina-based washcoat material with the chemically reactive material comprising a selective catalyst reduction catalyst. The selective catalyst reduction catalyst can comprise a silver alumina (hereafter “AgAl”) catalytic material, of a pre-selected weight percent of Ag₂O supported on an alumina washcoat. One range for the selective catalyst reduction catalyst can be applied at a 1 to 4 wt. % Ag in AgAl, with a washcoat loading in a range 0.5 to 4 g/in³ supported on the multi-channel substrate. Alternatively, the selective catalyst reduction catalyst can comprise copper on a washcoat at a copper mass loading and applied onto a substrate device. The coated substrate of the particulate filter device 20 is assembled into a metallic structure that is a part of the exhaust aftertreatment system.

The second catalytic device 24 depicted in the embodiments shown in FIGS. 2 and 3 preferably includes a selective catalyst reduction device comprising a multi-channel ceramic monolithic substrate coated with a catalytically reactive washcoat that reacts with the exhaust gas feedstream output from the particulate filter device 20. The catalytically reactive washcoat reacts with ammonia slip that can result from the NOx reduction occurring in the particulate filter device 20. The catalytically reactive washcoat can comprise a selective catalyst reduction catalyst comprising a copper-zeolite catalytic material of a pre-selected weight percent and supported on an alumina washcoat. The second catalytic device 24 provides reaction sites to reduce NOx in the exhaust gas feedstream using ammonia output from the catalytic device 14. The second catalytic device 24 may further include an oxidation catalyst, comprising a multi-channel ceramic monolithic substrate coated with a catalytically reactive washcoat containing Pt and/or Pd on Al₂O₃ washcoat. The loading of the washcoat may be 1-3 g/in³, with Pt loadings of 3-150 g/ft³.

The control module 5 is preferably an element of a distributed architecture comprising a plurality of control modules adapted to provide coordinated control of the engine 10 and other systems when the engine 10 and exhaust aftertreatment system are applied onto a vehicle (not shown). A user interface (‘UI’) 13 signally connects to a plurality of devices through which a vehicle operator controls and directs operation of the vehicle, including the engine 10. Exemplary devices through which the vehicle operator provides input to the user interface 13 include an accelerator pedal, a brake pedal, transmission gear selector, and vehicle speed cruise control, none of which are separately illustrated. The control module 5 preferably communicates with the user interface 13 via a local area network bus 6. The local area network bus 6 allows for structured communication of control parameters and commands between the various processors, control modules, and devices. The specific communication protocol utilized is application-specific.

The control module 5 comprises a general-purpose digital computer including a microprocessor or central processing unit, storage mediums comprising non-volatile memory including read only memory and electrically programmable read only memory, random access memory, a high speed clock, analog to digital and digital to analog circuitry, input/output circuitry, and devices and appropriate signal conditioning and buffer circuitry. The control module 5 has a set of control algorithms, comprising resident program instructions and calibrations stored in the non-volatile memory and executed to provide the respective functions for controlling the engine 10. The algorithms are preferably executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms are executed by the central processing unit and are operable to monitor inputs from the aforementioned sensing devices and execute control and diagnostic routines to control operation of actuators, using preset calibrations. Loop cycles are preferably executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, algorithms may be executed in response to occurrence of an event.

During operation of the engine 10, the control module 5 monitors inputs from sensing devices, synthesizes information, and executes algorithms to control actuators to achieve control targets, including fuel economy, emissions, performance, driveability, and protection of hardware. The engine 10 is preferably operated lean of stoichiometry, generating a lean exhaust gas feedstream that passes through the exhaust aftertreatment system.

The control module 5 monitors engine speed and load and air/fuel ratio to determine a mass flow concentration of NOx emissions, and controls the injection device 16 to control timing and mass or quantity of the hydrocarbon reductant injected into the exhaust gas feedstream based upon the mass flow concentration of NOx emissions. The quantity of the injected hydrocarbon reductant is controlled to react with the NOx emissions and reduce to nitrogen in the presence of the selective catalyst reduction catalyst.

The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims. 

1. An apparatus for treating an exhaust gas feedstream from an internal combustion engine, comprising: a particulate filter device comprising a porous substrate element having a hydrocarbon-selective catalytically reactive washcoat, the hydrocarbon-selective catalytically reactive washcoat comprising a silver-oxide catalytic material on an alumina-based washcoat.
 2. The apparatus of claim 1, further comprising an injection device operative to inject a hydrocarbon reductant into the exhaust gas feedstream upstream of the particulate filter device.
 3. The apparatus of claim 2, further comprising a second catalytic device fluidly connected downstream of the particulate filter device and comprising a substrate coated with copper-zeolite catalytic material on an alumina washcoat.
 4. The apparatus of claim 3, wherein the second catalytic device further includes an oxidation catalyst comprising a multi-channel ceramic monolithic substrate coated with a catalytically reactive washcoat containing at least one of platinum and palladium on an alumina washcoat.
 5. Apparatus, comprising: an internal combustion engine operative at an air/fuel ratio lean of stoichiometry and directly fluidly connected to an exhaust aftertreatment system; the exhaust aftertreatment system comprising an oxidation catalyst upstream of a particulate filter device; the particulate filter device including a hydrocarbon-selective catalytically reactive washcoat; and an injection device operative to inject a hydrocarbon reductant upstream of the particulate filter device.
 6. The apparatus of claim 5, wherein the hydrocarbon-selective catalytically reactive washcoat comprises a selective catalyst reduction catalyst supported on a washcoat material.
 7. The apparatus of claim 6, wherein the selective catalyst reduction catalyst comprises a silver-oxide catalytic material.
 8. The apparatus of claim 7, wherein the washcoat material comprises an alumina-based washcoat.
 9. The apparatus of claim 6, wherein a chemically reactive material of the selective catalyst reduction catalyst comprises copper.
 10. The apparatus of claim 5, further comprising the injection device operative to inject engine fuel.
 11. The apparatus of claim 5, further comprising a second catalytic device downstream of the particulate filter device.
 12. The apparatus of claim 11, wherein the second catalytic device comprises a selective catalyst reduction device.
 13. The apparatus of claim 5, wherein the internal combustion engine comprises a compression-ignition engine.
 14. The apparatus of claim 5, wherein the internal combustion engine comprises a spark-ignition engine selectively operative at a lean air/fuel ratio.
 15. The apparatus of claim 5, further comprising a sensing device operative to monitor an element of an exhaust gas feedstream in the exhaust aftertreatment system.
 16. An apparatus for treating an exhaust gas feedstream from an internal combustion engine operating lean of stoichiometry, comprising: an oxidation catalyst upstream of a particulate filter device and an injection device operative to inject a hydrocarbon reductant into the exhaust gas feedstream therebetween; and the particulate filter device comprising a monolithic substrate element constructed of a porous material and having a hydrocarbon-selective catalytically reactive washcoat.
 17. The apparatus of claim 16, wherein the hydrocarbon-selective catalytically reactive washcoat comprises a silver-oxide catalytic material in an alumina-based washcoat.
 18. The apparatus of claim 16, wherein the hydrocarbon-selective catalytically reactive washcoat comprises a copper-oxide catalytic material in an alumina-based washcoat. 